The invention relates to a combustion apparatus for a gas turbine engine. More particularly the invention relates to a wall structure for such a combustion apparatus, and to a wall element for use therein.
A typical gas turbine engine combustor includes a generally annular chamber having a plurality of fuel injectors at an upstream head end. Combustion air is provided through the head and in addition through primary and intermediate mixing ports provided in the combustor walls, downstream of the fuel injectors.
In order to improve the thrust and fuel consumption of gas turbine engines, i.e. the thermal efficiency, it is necessary to use high compressor pressures and combustion temperatures. This results in the combustion chamber experiencing high temperatures and there is therefore a need to provide effective cooling of the combustion chamber walls. Various cooling methods have been proposed including the provision of a doubled walled combustion chamber whereby cooling air is directed into a gap between spaced outer and inner walls, thus cooling the inner wall. This air is then exhausted into the combustion chamber through apertures in the inner wall. The exhausted air forms a cooling film which flows along the hot, internal side of the inner wall, thus preventing the inner wall from overheating.
The inner wall may comprise a number of heat resistant tiles, such a construction being relatively simple and inexpensive. The tiles are generally rectangular in shape and curved to conform to the overall shape of the annular combustor wall. The tiles are conventionally longer in the circumferential direction of the combustor than in the axial direction.
The tiles are typically of cast construction, while the outer xe2x80x9ccoldxe2x80x9d wall of the combustor wall structure is typically of sheet metal. Neither of these production methods produces components to very high tolerances and this inevitably results in gaps between adjacent tiles. It is also necessary to leave gaps between the edges of adjacent tiles, particularly the axially directed edges, in order to allow for expansion of the tiles in hot conditions. The air in the gap between the tiles and the outer cold wall is at a higher pressure than that inside the combustion chamber, and it is therefore inevitable that cooling air will leak into the combustion chamber through the axial gaps between adjacent circumferentially spaced tiles. The leaked air tends to form a relatively stiff, inwardly directed xe2x80x9cwallxe2x80x9d of air, which has a detrimental effect on the quality of the cool air film provided along the hot side of the tiles. As a result, overheating of the tiles may occur immediately downstream of the axial gap.
According to the present invention there is provided a wall structure for a gas turbine engine combustor arranged to have a general direction of fluid flow therethrough, the wall structure including inner and outer walls, the inner and outer walls define a space therebetween, wherein the inner wall includes a plurality of wall elements, the plurality of wall elements include axial edges aligned generally with the direction of fluid flow, a gap being defined between adjacent axial edges of adjacent tiles, and wherein means are provided for directing leakage air passing through the gaps such that the leakage air has a flow component in the general direction of fluid flow through the combustor.
Preferably at least one wall element includes a body portion and an axial edge portion, the body portion conforming to the general shape of the combustor wall structure and the axial edge portion including a member, the member extending from the body portion towards the outer wall of the combustor wall structure. The member may extend in a generally radial direction of the combustor.
The means for directing the leakage air may include at least one orifice, the at least one orifice provided in the axial edge portion of the wall element. Preferably the at least one orifice is provided in the member which extends from the body portion towards the outer wall of the combustor wall structure.
Preferably the orifices are directed at an angle of between 5xc2x0 and 70xc2x0 to the general direction of fluid flow through the combustor. Most preferably the orifices are directed at an angle of between 10xc2x0 and 45xc2x0 to the general direction of fluid flow through the combustor.
Preferably the at least one orifice lies generally parallel to the inner wall of the wall structure. The orifices may be cast into the wall element. Alternatively the orifices may be laser drilled into the wall element.
The axial edge portion may include a portion, the portion in use being overlapped by an axial edge portion of an adjacent wall element.
The wall structure may comprise at least two adjacent wall elements including peripheral edges, the edges being aligned generally across the direction of fluid flow, a gap being provided between adjacent peripheral edges of the adjacent wall elements, and wherein means are provided for directing leakage air passing through the gap such that the leakage air has a flow component in the general direction of fluid flow through the combustor. At least one wall element comprises a peripheral edge portion and a body portion, the edge portion including a member, the member extending from the body portion of the wall element towards the outer wall of the combustor wall structure, and the means for directing the leakage air may be provided within this member.
The wall element may be adapted for use in conjunction with other similar wall elements to form a wall structure.
According to the present invention there is further provided a wall element for use as part of an inner wall of a gas turbine engine combustor wall structure including inner and outer walls, the inner and outer walls defining a space therebetween, the wall element including axial edges, the axial edges aligned in use with a general direction of fluid flow through the combustor, wherein the wall element includes means associated with the axial edges for directing leakage air passing around the axial edges such that the leakage air has a flow component in the general direction of fluid flow through the combustor.
The wall element may include a body portion and an axial edge portion, the body portion conforming to the general shape of the combustor wall structure and an axial edge portion including a member, the member extending in use from the body portion towards the outer wall of the combustor wall structure, and wherein the means for directing leakage air includes at least one orifice, the at least one orifice provided in the axial edge portion of the tile.
According to the invention, there is further provided a gas turbine engine combustion chamber including a wall structure or wall element as defined in any of the preceding ten paragraphs.